De novo strategy of organic semiconducting polymer brushes for NIR-II light-triggered carbon monoxide release to boost deep-tissue cancer phototheranostics.

The integration of photoacoustic imaging (PAI) and photothermal therapy (PTT) within the second near-infrared (NIR-II) window, offering a combination of high-resolution imaging and precise non-invasive thermal ablation, presents an attractive opportunity for cancer treatment. Despite the significant promise, the development of this noninvasive phototheranostic nanomedicines encounters challenges that stem from tumor thermotolerance and limited therapeutic efficacy. In this contribution, we designed an amphiphilic semiconducting polymer brush (SPB) featuring a thermosensitive carbon monoxide (CO) donor (TDF-CO) for NIR-II PAI-assisted gas-augmented deep-tissue tumor PTT. TDF-CO nanoparticles (NPs) exhibited a powerful photothermal conversion efficiency (43.1%) and the capacity to trigger CO release after NIR-II photoirradiation. Notably, the liberated CO not only acts on mitochondria, leading to mitochondrial dysfunction and promoting cellular apoptosis but also hinders the overexpression of heat shock proteins (HSPs), enhancing the tumor's thermosensitivity to PTT. This dual action accelerates cellular thermal ablation, achieving a gas-augmented synergistic therapeutic effect in cancer treatment. Intravenous administration of TDF-CO NPs in 4T1 tumor-bearing mice demonstrated bright PAI signals and remarkable tumor ablation under 1064 nm laser irradiation, underscoring the potential of CO-mediated photothermal/gas synergistic therapy. We envision this tailor-made multifunctional NIR-II light-triggered SPB provides a feasible approach to amplify the performance of PTT for advancing future cancer phototheranostics.